In an image display device and the like, an image-forming scheme thereof essentially requires disposing a polarizing element on each of opposite sides of a liquid crystal cell. Generally, a polarizing film is attached thereto. When the polarizing film is attached to the liquid crystal cell, an adhesive is commonly used. As regards bonding between the polarizing film and the liquid crystal cell, respective materials thereof are generally bonded closely together through the adhesive so as to reduce light loss. In this case, an adhesive is employed because it has a merit such as being able to achieve fixing of the polarizing film without any need for a drying process. Typically, an adhesive is used in the form of an adhesive layer and polarizing film combination structure in which it is preliminarily provided as an adhesive layer on one surface of a polarizing film.
Meanwhile, late years, in an image display device for mobile applications such as a mobile phone, an entire display module thereof tends to be reduced in thickness and weight more and more, particularly, from aesthetic performance and portability. A polarizing film for use in the image display device also needs to be further reduced in thickness and weight. On the other hand, an image display device is increasingly used in various environments such as an outdoor or harsh environment, and is therefore sought to have higher durability than before. Because of the above circumstances, there is a need for a thinned polarizing film having excellent optical properties, and it is also necessary to develop an adhesive layer applicable to such a thinned polarizing film.
In a process for attaching a polarizing film to a liquid crystal cell, first of all, a separator (release film) laminated to a surface of the polarizing film through an adhesive layer is peeled off to expose the adhesive layer, and then the polarizing film is laminated to a liquid crystal display panel. In this process, it is common to, in a state in which the polarizing film is suckingly held on a surface of a stage, attach a peeling tape to a surface of the separator (release film) at one end thereof, and pull the peeling tape toward the other end of the separator to thereby peel off the separator from the polarizing film.
With a view to enhancement in durability and others, it is often the case that a cross-linking agent is added to an adhesive composition for forming the adhesive, e.g., together with a (meth)acryl-based polymer. For example, the following Patent Document 1 describes an adhesive which contains a peroxide and an isocyanate-based compound, in addition to a (meth)acryl-based polymer. In the following Patent Document 2 also describes an adhesive which contains a peroxide and an isocyanate-based cross-linking agent, in addition to a (meth)acryl-based polymer containing a (meth)acryl-based monomer and a nitrogen-containing monomer. The Patent Document 3 describes a method of producing a silicone-coated release liner-attached adhesive layer. The method comprises: a first step of providing a layer of an adhesive composition containing a (meth)acryl-based polymer serving as a base polymer and a peroxide, on a release treatment surface (surface subjected to a release treatment) of a silicone-coated release liner; and a second step of, after completion of the first step, thermally decomposing a part or an entirety of the peroxide to adjust a peel force of the silicone-coated release liner.